How it's calculated
The original Centor criteria score 1 point each for tonsillar exudate, tender cervical nodes, fever, and absence of cough. The McIsaac modification adds an age adjustment (+1 for ages 3-14, −1 for ages 45+), extending the score's validated use down into children.
Score interpretation
| Score | Estimated strep probability | Suggested action |
|---|---|---|
| ≤0 | 1–2.5% | No testing or antibiotics |
| 1 | 5–10% | No testing or antibiotics |
| 2 | 11–17% | Consider rapid strep test |
| 3 | 28–35% | Consider rapid strep test or empiric treatment |
| ≥4 | 51–53% | Consider empiric antibiotic treatment |
Clinical use
- The Centor/McIsaac score helps avoid unnecessary antibiotics for the majority of sore throats, which are viral, by identifying patients where Group A streptococcus is likely enough to justify testing or treatment.
- A rapid antigen detection test (or throat culture) at intermediate scores (2-3) is generally preferred over empiric antibiotics, to avoid overtreatment.
- The McIsaac age adjustment is what allows this score to be used in children as young as 3, unlike the original adult-only Centor criteria.
- Even with a high score, most "strep throat" is self-limiting — antibiotics mainly shorten symptom duration modestly and reduce (rare) suppurative complications, rather than being essential to recovery.
Frequently asked questions
What is the Centor score used for?
It estimates the probability that a sore throat is caused by Group A streptococcus, helping decide whether testing or antibiotics are worthwhile, since most sore throats are viral and don't need either.
What is the difference between Centor and McIsaac scores?
The McIsaac score adds an age adjustment to the original Centor criteria — an extra point for children aged 3-14, and a point subtracted for adults 45 and older — extending validated use of the score into younger patients.
Does a high Centor score mean antibiotics are definitely needed?
Not automatically — a high score increases the probability of strep, at which point either a rapid test to confirm before treating, or empiric treatment, are reasonable options depending on local practice and test availability.
Why is absence of cough part of the score, rather than presence of cough?
Cough is more typical of a viral cause; its absence — alongside fever, exudate, and lymphadenopathy — points more specifically toward a bacterial (streptococcal) cause.
References
- Centor RM, et al. The diagnosis of strep throat in adults in the emergency room. Med Decis Making. 1981;1:239-246.
- McIsaac WJ, et al. A clinical score to reduce unnecessary antibiotic use in patients with sore throat. CMAJ. 1998;158:75-83.
- Shulman ST, et al. Clinical Practice Guideline for Group A Streptococcal Pharyngitis (IDSA). Clin Infect Dis. 2012;55:e86-e102.